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When I try to upgrade or install a plugin I get a successful message:

Downloading install package from http://downloads.wordpress.org/plugin/jquery-lightbox-gallery.zip…

Unpacking the package…

Installing the plugin…

Successfully installed the plugin Fancy Gallery 1.0.27.

Activate Plugin | Return to Plugin Installer`

If however I have a look via ftp in my plugins directory the plugin has not been installed and the new plugin folder does not exist.

Then when I click the Activate Plugin link I get the following error The plugin does not have a valid header. which is not surprising considering the plugin hasn't been installed.

This happens no matter which plugin I try to install. It's strange because I have several other wordpress installations on the same host, and infact two other separate wordpress installations on the same domain and I have never had this problem.

I tried re-uploading a fresh installation of wordpress over the top of the current one and there was no change. I tried deactivating every single plugin and switching to the basic theme but it still didn't work. Any help would be greatly appreciated!

Update: So I tried making a new FTP account, and I can now add plugins using this new account. However when I try to upgrade a plugin I still get a Could not remove the old plugin. Plugin update failed. error.

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closed as too localized by Rarst May 27 '13 at 12:55

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

    
It is a long shot, but try switching themes to rule out a theme problem. –  Charles Clarkson May 12 '13 at 21:32
    
Thanks for the suggestion. I just tried it, but that didn't help either. –  Nick5a1 May 13 '13 at 5:02
    
So I tried making a new FTP account, and I can now add plugins using this new account. However when I try to upgrade a plugin I get a Could not remove the old plugin. Plugin update failed. error. –  Nick5a1 May 13 '13 at 21:50
    
To anyone with the same problem - I don't know what caused it, but I got my host to switch me over to FastCGI (which eliminates the need for correct file permissions and ownership) and it now works. –  Nick5a1 May 14 '13 at 17:22
    
@Nick5a1 Please add your solution as an answer and accept it –  bungeshea May 16 '13 at 11:00
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